Machinability evaluation and desirability function optimization of turning parameters for Cr2O3 doped zirconia toughened alumina (Cr-ZTA) cutting insert in high speed machining of steel

Abstract

In present study, mechanical properties, microstructure and machining parameter optimization of Cr2O3 doped zirconia toughened alumina (ZTA) ceramic insert have been investigated for application in high speed turning of AISI 4340 steel with achieving maximum tool life. The yttria stabilized zirconia (YSZ) in α-Al2O3 matrix with varying percentage of co-doped chromia (Cr2O3) is prepared to study the phase transformation behaviour. The samples are uniaxially pressed in the form of cutting inserts and subsequently sintered at 1600°C to evaluate the mechanical properties. Hardness and fracture toughness reaches the highest value i.e. 17.40GPa and 7.20MPam1/2 respectively at 0.6% Cr2O3 doped ZTA due to more metastable tetragonal ZrO2 phase present in the alumina matrix. After 50min of machining, the flank wear and surface roughness are found well below the tool rejection criteria. The cutting force also does not affect detrimentally on the job–tool interface. Turning experiments have been adopted as per central composite design (CCD) of response surface methodology (RSM) with varying 3 levels of cutting speed (140m/min, 280m/min, 420m/min), feed rate (0.12mm/rev, 0.18mm/rev, 0.24mm/rev) and depth of cut (0.50mm, 1.00mm, 1.50mm). The effect of each input parameter on output responses is investigated using analysis of variance (ANOVA) and modelled using regression analysis. The influence of cutting speed, feed rate and depth of cut is observed maximum for determination of flank wear, cutting force and surface roughness respectively. Cutting speed of 420m/min with feed rate of 0.12mm/rev and depth of cut of 0.5mm has been shown as optimized condition with 83.32% desirability for minimum tool failure and maximum tool life.